This invention relates to a pneumatic brake control device which is used in the electric cars of railroad vehicles, and it normally supplements any insufficiencies in the electric braking force portion of the total braking force; and when this electric braking force becomes ineffective, then it provides the total braking force.
A known arrangement (as shown in FIG. 3) includes dispatch lines SB1, SB2, and SB3 over which a 3-bit digital electrical signal (brake command) is given by the brake controller (not shown), a brake command receiver 1 consisting of the normal first receiver 11 and the backup second receiver 12, an electrical braking device EB, an electric-pneumatic converter EP, a multi-way valve RV with solenoid valves MV1, MV2, and MV3, a brake cylinder BC, and a source of compressed air MR.
The first receiver 11 has the receiver RE, the brake force pattern set-up device BS, and the operator OP, and receives the brake command signal, transmitting it to the electrical brake device EB; and at the same time, the electrical signal (equivalent dispatch) corresponding to the actual electrical braking force is fed back from the electrical brake device EB, and the equilavent signal is subtracted from the brake command signal at the operator OP, and the result is transmitted to the electric-pneumatic converter valve EP as the first supplementary brake command signal.
The second receiver 12 includes a detection relay R, which demagnetizes in response to any loss of the power source or an abnormal voltage-drop below a defined value. The contact point Ra of relay R is normally open, and its contact Rb is normally closed. When the power source is operating normally, the contacts Ra and Rb are in the positions shown in the FIGURE. Under abnormal power source conditions, the normally open contact Ra is open and interrupts operation of the first receiver 1 and, at the same time, the normally closed contact port Rb is closed and the brake command signal is transmitted to the solenoid valves MV1, MV2, and MV3 as the second supplementary brake command.
Since the electric-pneumatic converter valve EP, the solenoid valves MV1, MV2, and MV3, and the multi-way connection valve RV are well known, an explanation of these devices will not be undertaken here.
As described above, a conventional brake control device for electric cars outputs an electrical signal according to the deficit portion of the electrical braking force in relation to the total braking force via the first receiver 11, when the power source of the first receiver 11 is normal, as the first supplementary command, and this signal is converted to air pressure by the electric-pneumatic converter valve EP. Based on the air pressure, the pressure of the brake cylinder BC is regulated and when the power source of the receiver 11 becomes abnormal, the brake command is output as the second supplementary command by the second receiver 12 acting as a backup, and this is converted to air pressure by the multi-way valve RV with solenoid valves, and based on this air pressure, the pressure of the brake cylinder BC is controlled.
In the arrangement according to the prior art described above, since the malfunction of the first receiver 11 is evaluated solely as a function of the anomaly of the power source, if the power source is normal but for example, the operator OP controlling the first receiver 11 malfunctions, then the second supplementary command by the second receiver 12, namely the backup brake command, is not output, and hence, the reliability of the pneumatic brake device is low. Also, due to the fact that the multi-way valve RV including the solenoid valves MV1, MV2, and MV3, provide backup service and are therefore used only occasionally in order to convert the second supplementary brake command to air pressure, the weight and the space occupied, as well as the initial costs cannot be justified. Also, there is the problem of high cost for the performance of maintenance and inspections which must be done periodically, irrespective of the amount of use.